Plasma processing apparatus

ABSTRACT

In one aspect there is provided a plasma processing apparatus including a substrate placing unit configured to be placed a substrate to be processed, and an upper electrode opposed to the substrate placing unit, wherein an outer portion of a main surface of the upper electrode opposed to the substrate placing unit has a mirror surface.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2013-028420, filed on Feb. 15, 2013, the entire contents of which are incorporated herein by reference.

FIELD

Exemplary embodiments described herein generally relate to a plasma processing apparatus.

BACKGROUND

Conventionally, etching a substrate to be processed has been performed by using a plasma processing apparatus as one process in fabricating a semiconductor device. In plasma processing apparatus, which is a semiconductor production apparatus, Reactive Ion Etching (RIE) or the like is conducted. An upper electrode made of silicon opposed to the substrate to be processed is placed in the plasma processing apparatus.

A surface of the upper electrode may be etched by etching gas of plasma state in the plasma processing apparatus in which plasma is generated between the upper electrode and the substrate to be processed.

A portion roughed in the surface of the upper substrate is focused with electric field to be further etched so that the roughed portion may be largely removed compared to the nearby portion when an upper electrode with larger roughness is utilized. The etching gas in plasma state inserts into an area between the upper electrode and a supporting unit of the upper electrode to etch a back surface of the upper electrode.

Accordingly, a problem described below has been pointed out in technique using plasma processing. Dusts, which are made of a material of the upper electrode, are generated in a chamber of the plasma processing apparatus. Consequently, the dusts are adhered to the substrate to be processed in the etching process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a plasma processing apparatus according to an embodiment;

FIGS. 2A-2B are cross-sectional views showing an upper electrode according the embodiment.

DETAILED DESCRIPTION

An aspect of the present embodiment, there is provided a plasma processing apparatus including a substrate placing unit configured to be placed a substrate to be processed, and an upper electrode opposed to the substrate placing unit, wherein an outer portion of a main surface of the upper electrode opposed to the substrate placing unit has a mirror surface.

Embodiments will be described below in detail with reference to the attached drawings mentioned above. Throughout the attached drawings, similar or same reference numerals show similar, equivalent or same components, and the description is not repeated. Further, a film described in embodiments below, for example, is schematically shown. Accordingly, a relation between a thickness of the film and a width of the film, a ratio between each of films or the like is different from a real value.

Embodiment

FIG. 1 is a cross-sectional view schematically showing a plasma processing apparatus according to an embodiment. RIE apparatus is described as a plasma processing apparatus 10, for example. The plasma processing apparatus 10 has a vacuum chamber 11 which is generally made from aluminum. The chamber 11 is electrically grounded.

A supporting table 21 is placed to horizontally support a substrate W to be processed as a process object in the chamber 11 and has a function as a lower electrode. A holding unit (not shown) such as an electrostatic chuck unit to absorb the substrate W to be processed or the like is placed on a surface of the supporting table 21. An insulating ring 22 is provided to cover periphery portions of both a sidewall and a bottom wall of the supporting table 21. An edge ring 23 is provided on an outer periphery at an upper portion of the supporting table 21 covered with the insulating ring 22. The edge ring 23 is a member to adjust electric field in etching process of the substrate W to be processed. The electric field is not deviated in vertical direction to a periphery portion of the substrate W to be processed, in other words, in a perpendicular to the surface of the substrate to be processed, by using the edge ring 23.

The supporting table 21 is fixed by a supporting unit (not shown) supported by the chamber 11 to be placed at a position near the center of the chamber 11. An insulating ring 22 is placed on a periphery portion of the supporting table 21. A power supply line 31 is connected to the supporting table 21 to supply radio frequency power. A blocking condenser 32, a matching box 33 and a high frequency power 3 are connected to the power supply line 31. Radio frequency power with a prescribed frequency is supplied to the supporting table 21.

An upper electrode is provided at an upper portion of the supporting table 21 and is opposed to the supporting table 21 acting as the lower electrode. The upper electrode is in parallel to the supporting table 21 and is fixed to a member 41 near an upper portion of the chamber 11 separated a prescribed distance from the supporting table 21. In such a structure, the upper electrode and the supporting table 21 constitutes a pair of a parallel plate electrode. A plurality of gas supply paths penetrating into the upper electrode in the thickness direction is provided at an inner edge portion of the upper electrode. The upper electrode has a circular shape, for example. The upper electrode is composed of silicon, for example.

A gas inlet 12 is provided near an upper portion of the chamber 11. Process gas used in plasma processing is supplied from the gas inlet 12. A gas supply unit (not shown) is connected to the gas inlet 13 through pipes.

A gas outlet 13 is provided at a lower portion of the supporting table 21. A vacuum pump (not shown) is connected to the gas outlet 13 through pipes.

An area between the supporting table 21 and the upper electrode in the chamber 11 is plasma processing space 51. An area at an under portion between the supporting table 21 and the bottom portion of the chamber 11 is a gas exhaust unit 52.

An outline of processing steps by using the plasma processing apparatus 10 constituted described above is explained. The substrate W to be processed as a processing object is placed on the supporting table 21 to be fixed with the electrostatic chuck unit. The chamber 11 is evacuated by the vacuum pump (not shown) connected to the gas outlet 13.

When the chamber 11 reaches a prescribed pressure therein, process gas is supplied from the gas supply unit (not shown) to a gas supply area further to supply the process gas to the plasma processing space 51 through the gas supply path in the upper electrode. When the plasma processing space 51 reaches a prescribed pressure therein, radio frequency power is applied to the supporting table 21 (lower electrode) to generate plasma in the plasma processing space, in a state that the upper electrode is electrically grounded. As the radio frequency voltage is applied to the lower electrode, an electrical potential gradient is generated between plasma and the substrate to be processed to accelerate ions in plasma to the supporting table 21. As a result, the etching processing is conducted.

FIGS. 2A-2B are cross-sectional views showing an upper electrode according the embodiment. The sidewall with a taper and a convex portion 42 a including a portion of main surface faced to the substrate W to be processed are provided at the outer portion of the upper electrode. The sidewall and the main surface of the convex portion 42 a are polished to produce a mirror surface. Roughness of the surface is not more than 100 nm in average. In such a manner, it can be avoided that the surface of the upper electrode is focused with electric field during the plasma processing in the chamber 11. Accordingly, it is prevented that the upper electrode is over-etched so that dusts are scattered in the chamber 11.

Furthermore, an outer portion of a back surface of the upper electrode, in other words, a counter surface to the surface opposed to the substrate to be processed 52 can be polished to be mirror. Roughness of the back surface of the upper electrode after polished to be mirror is not more than 100 nm in average. In the upper electrode, a member 41 in which the gas supply paths penetrating into the member 41 in the thickness direction is provided. Generally, the back surface of the upper electrode is rough to be etched by the etching gas in the plasma processing. In a case that the back surface of the upper electrode is polished according to the embodiment, an adherence between the member and the upper electrode is improved. Therefore, it is suppressed that the gas in a plasma state immerses a space between the upper electrode and the member 41. In such a manner, the etching of the upper electrode by the etching gas is suppressed so that the dusts can be controlled to not to scatter in the chamber 11. Especially, only the outer portion 42 b of the back surface of the upper electrode can be polished to be a mirror state. In such a manner, the adherence between the upper electrode and the member 41 is improved to be higher, so that the gas in the outer portion immersing between the upper electrode and the member can be suppressed.

As described above, the surface of outer portion of the upper electrode is mirror-polished according to the plasma processing apparatus. In such a manner, it can be suppressed that the rough portion of the surface is focused with electric field to etch the focused portion, so that the dusts generated from the upper electrode scatter in the chamber 11. Furthermore, the outer portion of the upper electrode is not necessary to be provided the convex portion 42 a.

Further, the back surface of the upper electrode is processed to be mirror according to the embodiment. In such a manner, the back surface of the upper electrode and the member at the upper portion of the upper electrode are bonded with high adherence. Accordingly, it can be suppressed that the etching gas is immersed between the upper electrode and the member in the plasma processing. Namely, the etching of the upper electrode can be controlled to suppress scattering of the dusts in the chamber.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 

What is claimed is:
 1. A plasma processing apparatus, comprising: a substrate placing unit configured to hold a substrate to be processed; and an upper electrode opposed to the substrate placing unit; wherein an outer portion of a main surface of the upper electrode opposed to the substrate placing unit has a mirror surface.
 2. The plasma processing apparatus of claim 1, wherein roughness of the outer portion of the main surface is not more than 100 nm.
 3. The plasma processing apparatus of claim 1, wherein the outer portion of the main surface has a convex shape.
 4. The plasma processing apparatus of claim 3, wherein a sidewall of the convex shape has a taper shape.
 5. The plasma processing apparatus of claim 1, wherein a back surface opposed to the main surface of the upper electrode has a mirror surface.
 6. The plasma processing apparatus of claim 1, wherein an outer portion of the back surface has a mirror surface.
 7. The plasma processing apparatus of claim 6, wherein roughness of the outer portion of the back surface is not more than 100 nm. 